Improved Hybrid FDTD Method for Studying Tunable Graphene Frequency-Selective Surfaces (GFSS) for THz-Wave Applications

One hybrid finite-difference time-domain (FDTD) method is proposed for studying transmission characteristics of a THz wave through some tunable dispersive graphene frequency-selective surfaces (GFSSs) biased by an electrostatic or a magnetostatic field, respectively. It integrates auxiliary differential equation (ADE)-FDTD with high-order conformal FDTD (2, 4) so as to handle atomically thin periodic structures on an electrically anisotropic substrate with high flexibility and accuracy. The dispersion error and computational efficiency of the developed algorithm is validated in comparison with the piecewise linear recursive convolution (PLRC)-FDTD and commercial software HFSS, respectively. Numerical studies are further performed to demonstrate its capability for characterizing the effects of chemical potential of graphene, biasing electrostatic and magnetostatic fields, and geometrical parameters of different GFSSs on the central frequencies and 3-dB bandwidths of their passbands and stopbands. In particular, both frequency selectivity and tunability of GFSSs made of single- and double-layer periodic split-ring resonators are predicted, which can be exploited for developing some novel tunable THz structures.